Use a different way to get the size of structs with flexible array members

3 files changed, 9 insertions, 7 deletions

diff --git a/OpenAL32/Include/alMain.h b/OpenAL32/Include/alMain.h
index 191bb658..3a8aabde 100644
--- a/OpenAL32/Include/alMain.h
+++ b/OpenAL32/Include/alMain.h
@@ -225,6 +225,12 @@ typedef ALuint64SOFT ALuint64;
 #define DECL_FORMAT(x, y, z)
 #endif
 
+/* Calculates the size of a struct with N elements of a flexible array member.
+ * GCC and Clang allow offsetof(Type, fam[N]) for this, but MSVC seems to have
+ * trouble, so a bit more verbose workaround is needed.
+ */
+#define FAM_SIZE(T, M, N)  (offsetof(T, M) + sizeof(((T*)NULL)->M[0])*(N))
+
 #if defined(__GNUC__) && defined(__i386__)
 /* force_align_arg_pointer is required for proper function arguments aligning
  * when SSE code is used. Some systems (Windows, QNX) do not guarantee our
diff --git a/OpenAL32/alAuxEffectSlot.c b/OpenAL32/alAuxEffectSlot.c
index 3ec857ca..5d110500 100644
--- a/OpenAL32/alAuxEffectSlot.c
+++ b/OpenAL32/alAuxEffectSlot.c
@@ -118,9 +118,7 @@ AL_API ALvoid AL_APIENTRY alGenAuxiliaryEffectSlots(ALsizei n, ALuint *effectslo
         ALsizei newcount = curarray->count + n;
         ALCdevice *device;
 
-        newarray = al_calloc(DEF_ALIGN,
-            offsetof(struct ALeffectslotArray, slot[newcount])
-        );
+        newarray = al_calloc(DEF_ALIGN, FAM_SIZE(struct ALeffectslotArray, slot, newcount));
         newarray->count = newcount;
         memcpy(newarray->slot, tmpslots, sizeof(ALeffectslot*)*n);
         if(curarray)
@@ -170,9 +168,7 @@ AL_API ALvoid AL_APIENTRY alDeleteAuxiliaryEffectSlots(ALsizei n, const ALuint *
         ALsizei j, k;
 
         assert(newcount >= 0);
-        newarray = al_calloc(DEF_ALIGN,
-            offsetof(struct ALeffectslotArray, slot[newcount])
-        );
+        newarray = al_calloc(DEF_ALIGN, FAM_SIZE(struct ALeffectslotArray, slot, newcount));
         newarray->count = newcount;
         for(i = j = 0;i < newarray->count;)
         {
diff --git a/OpenAL32/alSource.c b/OpenAL32/alSource.c
index 236188cf..9fc22205 100644
--- a/OpenAL32/alSource.c
+++ b/OpenAL32/alSource.c
@@ -3013,7 +3013,7 @@ static void UpdateSourceProps(ALsource *source, ALvoice *voice, ALsizei num_send
     /* Get an unused property container, or allocate a new one as needed. */
     props = ATOMIC_LOAD(&voice->FreeList, almemory_order_acquire);
     if(!props)
-        props = al_calloc(16, offsetof(struct ALvoiceProps, Send[num_sends]));
+        props = al_calloc(16, FAM_SIZE(struct ALvoiceProps, Send, num_sends));
     else
     {
         struct ALvoiceProps *next;